In this week’s Budget, the Chancellor, Phillip Hammond, announced a new VED policy for diesel cars. Under the new rules, all new diesel cars that do not meet RDE2 standards, will move up by one VED bracket.

So, what is RDE2? And what could this mean for improving air quality?

What is an RDE2 diesel?

When a new car is certified for sale in the UK and Europe, it must undergo strict emissions testing. Current standards state that, under standard laboratory testing, a new diesel or petrol car must emit no more than 0.080g/km of nitrogen oxide (NOx).

RDE stands for Real Driving Emissions. This is the test that can be used by vehicle manufacturers to test the emissions a car produces under real driving conditions (e.g. not in a laboratory).

RDE was introduced in September 2017 and, at the moment, OEMs have the option of putting new cars through the test, in addition to the standard laboratory emissions test. It will not be mandatory for all new cars to be put through RDE until September 2019.

However, because there is an expected difference between emissions from a car in the laboratory and under real world testing, there are different stages of RDE.

The first stage allows a car to emit 2.1 times the amount of NOx during RDE testing.

The second stage, RDE2, allows cars to emit 1.5 times the amount of NOx during RDE testing. This becomes mandatory for all cars on sale by January 2021.

Is RDE2 the only clean diesel?

On paper, RDE2 diesels will be the lowest-emitting diesel cars ever on sale.

However, in reality, the issue is more complex. An RDE2 diesel will be able to emit up to 0.120g/km NOx under the RDE test. Yet, data from Emissions Analytics shows that there are already non-RDE diesels on sale that emit less than this.

The EQUA Aq Index, powered by Emissions Analytics, rates the real-world NOx emissions of every new car on sale today. A car that it rated as A+ emits 0.060g/km NOx, while an A-rated car emits 0.080g/km NOx in the real world.

There are currently more than 20 A+ and A-rated diesel cars featured on the EQUA Aq Index, all of which will be subject to the Chancellor’s new VED hike.

Will the new Budget policy on diesel improve air quality?

The new Budget policy may have some impact on air quality. However, with RDE2 not due to come into full force for more than four years (2021), the results won’t be felt for some time.

There is also some concern within the automotive industry about the negative impact this measure will have on new diesel sales.

The Budget announcement is a significant acknowledgement from government that not all Euro-6 diesels are as good as each other. However, this will be an unfair penalty on the small number of manufacturers that are already selling genuinely clean diesels. This will likely impact on diesel car sales and residual values, without tackling the real air quality issue caused by older, dirty diesels.

Nick Molden, Founder and CEO of Emissions Analytics

Click here for a full rundown of all the major automotive announcements from this week’s Budget.

This story was written by automotive PR specialists Torque Agency Group.